Electric fuse



Nov. 27, 1934. w. A. STOEHR 1,982,032

ELECTRIC FUSE Filed May 13, 1933 Patented Nov. 27, 1934 UNITED STATES PATENT OFFICE ELECTRIC FUSE Application May 13, 1933, Serial No. 670,820

3 Claims.

My present invention relates to electric fuses which are screwed into position in the cut-out box, switch board or other mounting.

Electric fuses are introduced into circuits to protect the latter against dangerous rises in amperage, a fusible element blowing or melting and thus interrupting the circuit when such rises occur, and the circuit must again be completed by a replacement of the fuse before the A supply of current is reestablished therein.

Frequently irresponsible persons attempt to bridge the gap and reestablish the circuit caused by the blowing of the fusible element, by substituting for the fusible element a piece of wire, a

1 coin or other piece of conductive material. This efiects a reestablishment of the circuit but destroys the protective function of the fuse as the make-shift bridge will carry a higher amperage than that for which the circuit is intended.

Therefore one of the objects which I have in view is the provision of a fuse device so constructed that after the fusible element has been blown, it can not be replaced by any make-shift bridge and the circuit can only be reestablished s by means of a proper replacement.

This object I effect by means of my improved fuse.

Again in an attempt to prevent the circuit being interrupted, frequently thoughtless persons so replace the fusible element by one arranged to carry a higher amperage than that for which the circuit is designed, thus again destroying the protection which the fuse is intended to afford.

Therefore another object which I have in view is tc'prevent the substitution in an electric fuse of a fusible element of higher amperage capacity than that for which the fuse is designed.

This object I effect by so arranging the coacting parts of the adapter and plug of my electric fuse that a given adapter will only receive and seat a plug having a fusible element of the proper amperage.

Again, through carelessness or a desire to cause the circuit to carry a greater amperage than it is designed for, the entire fuse is sometimes unscrewed from its socket in the fuse box or other mounting and a fuse designed to carry a greater amperage is substituted, thus again destroying the safety feature.

Therefore another object which I have in view is the prevention of such unauthorized substitution and I effect this object by providing the adapter of my electric fuse with locking means whereby after the adapter has been screwed into (Cl. 200l19) position it can not be removed by unauthorized persons.

Other objects and means for effecting the same will appear from the following description.

In the accompanying drawing wherein I have illustrated a practical embodiment of the principles of my invention, Fig. 1 is a plan view of a portion of a cut-out box with a fuse mounted therein.

Fig. 2 is a longitudinal sectional view through the assembled fuse, the same being taken along the line 22 in Fig. 4.

Fig. 3 is a plan view of the adapter member of the fuse, looking from above in Fig. 2.

Fig. 4 is a cross sectional view taken along the line 4-4 in Fig. 2.

Fig. 5 is an elevation of the plug member of the fuse.

Referring to the drawing, 1 represents the mounting for the fuse, such as the cut-out box,

switch board or the like, the same being provided with the usual screw socket into which the fuse is screwed.

The fuse comprises an adapter member 2 and a plug member 3, both formed of suitable nonconductive material.

The adapter is provided with a cylindrical bore 4 which is closed at its inner end. The end wall of the adapter member is provided with a contact button 5 whose stem 6 extends through the end wall of the adapter member and has fixed to its inner end the usual bent leaf spring 7. 8 is the usual metal ferrule mounted on the adapter member and provided with the screw threads by means of which the fuse is mounted in the cut-out box.

The plug member 3 is provided with a cylindrical stem portion of proper diameter to fit into the bore 4 of the adapter member 2 and also with a circumferentially extended head 9.

The stem and head of the plug member may be formed of one piece or the outer end of the stem may be forced into the bore of the head and suitably secured in place. The inner end of the bore of the stem is closed and on its exterior surface is provided with a metal contact button 10 mounted on the end of a pin 11 which extends through the end wall of the stem. The other or outer end of the stem is provided with a transversely disposed groove 12 and in said groove is located the fusible link 13 having its center reduced to localize fusion. One end of the link 13 is prolonged to form a leg 14 which extends along the bore of the stem and is connected as by soldering to the inner end of the pin ing the circuit.

11. The other end of the fusible link 13 is connected to a pin 15 which extends down through a small bore 16 in the wall of the plug and intersects with a seat 1'7 cut through the wall of the stem and in which is fixed a metal stud 18. The pin 15 extends into a hole in the stud 18 and is soldered therein. The stud l8'prot rudes laterally from the stem of the plug andis preferably provided with a rounded outer end. The bore of the adapter 2 is provided with a longitudinally disposed groove 19 which furnishes clearance for the stud 18 when the plug is pushed into the adapter.

The bore of the adapter is also provided adjacent its inner end with an annular groove 20 disposed in a plane at right angles to the axis of the adapter, and for substantially 180 of its extent said groove is out clear through the wall of the adapter, as illustrated at 21 in Fig. 4, the ends of said cut away portion indicated at 22 and 23 forming stop. shoulders. The lower end of the longitudinal groove 19 merges into the groove 20.

Rotatably mounted in said groove 20 is a filler ring 25 and said ring is provided with a segmental shoulder 26 which extends radially into the cut-out portion 21 of the groove. The segment 26 by coming into contact with either the shoulder 22 or 23, as the ring is rotated in its seat, limits the arc of movement of the filler ring 25.

The filler ring 25 is interrupted as at 28, the gap being of sufficient width to receive the protruding end of the stud 18 as the plug is pushed into the adapter. When the spacer ring 25 is in position wherein its segment 26 abuts against the shoulder '23, its gap 28 registers with the vertical slot 19, and the plug 3 may be inserted into the adapter until the stud 18 occupies the gap 28 of the spacer ring. The plug is rotated, rotating with it the spacer ring 25, until said ring assumes the position shown in Figs. 2 and 4 with the segment 26 abutting against the shoulder 22. Opposite this position of the gap 28 and the stud 18, the wall of the adapter is cut away to form an opening 29 through which a bent spring contact member 30 extends inwardly. The other end of the spring is soldered to the inner wall of the ferrule 8. When the plug is turned into its position shown in Figs. 2 and 4 the stud 18 makes a good electrical contact with the spring 30, and the spring is in itself in electrical contact with the ferrule 8. When the plug is in place its button 10 is pressed into contact with the bent spring 7, and thus the fusible link 18 is in circuit.

The head 9 of the plug is provided with a central opening 81 of greater diameter than the bore of the stem in which is fixed the metal frame Y 32 for the sight-mica 33, back of which the link 13 is exposed to view.

In service the current passes through the fusible link and when a rise in amperage above the safety limit occurs the link is fused, thus break In such case the plug is removed by rotating it from its position shown in Figs. 2 and 4 into a position wherein the gap 28 and the stud 18 register with the lower end of the slot 19, whereupon the plug may be pulled out of the adapter and a new plug pushed into the adaptthe detent will be deflected and trail. However,

socket.

after the fuse is screwed into place, an attempt to rotate the adapter in the opposite direction, to

unscrew it from its socket, will cause the sharpened end of the detent to dig into the wall of the Thus when once installed in its socket the adapter cannot be removed therefrom without breaking it into pieces, as the detent looks it against removal.

It is thus apparent that an unauthorized person cannot remove the adapter without destroyiig it.

It is also evident that in case the fusible element 13 be blown and the plug be withdrawn from the adapter, the contact points of the lat-. ter, viz. the button 7 and the spring 30 cannot be connected or bridged by the insertion of a piece of wire, a coin or other article of conductive material, but the fuse may be restored to service only by the insertion into the adapter of a suitable plug with an intact fusible element.

To prevent a plug adapted to carry a greater amperage than that intended for the circuit from being inserted into the adapter, I construct the fuses designed for different amperages with different locations of the groove 20 relative to the bore 4 of me adapter and correspondingly different locations of the stud 18 on the plug 8, so that only a plug of the proper amperage can be used with the corresponding adapter. Thus unauthorized persons are unable to destroy the protection by substituting fuses capable of carrying currents greater than those for which the circuit is intended.

To avoid confusion and to facilitate the assembling of the fuses and the insertion of a plug of the proper character into the corresponding adapter, I color the adapters and plugs of the same amperage alike and those of different amperages are of contrasting colors.

It is thus seen that my improved fuse is both non-transferrable and non-interchangeable.

It is obvious that when the plug is withdrawn the filler ring 25 is in position to cover and mask the spring 30, and the filler ring is held resiliently in its position by the pressure of the spring against the perimetral surface of the ring.

1. In an electric fuse, the combination of an adapter having a longitudinal bore with a longitudinally disposed groove in the sidewall there- 135 of and an annular seat in the wall of the bore 'at the inner end of the groove, electrical contact means exposed in said groove, a plug arranged to be inserted in said bore, a second contact means projecting from the plug which engages said groove while the plug is being inserted and which is caused to move along said seat into contact with the first mentioned contact means by the rotation of the inserted plug, a filler ring rotatably mounted in said seat and gapped to receive the second contact means, and a fusible element carried by the plug and electrically connected with the second contact means.

2. In an electric fuse, the combination of an 150 adapter having electric contact means arranged to engage the contact means of a socket into which the adapter is screwed, and provided with a cylindrical bore closed at one end, a plug provided with a fusible element and arranged to be inserted in said bore, contact elements at the lower end of the bore and at the lower end of the plug which engage when the plug is inserted into the bore, the contact element at the lower end of the plug being connected to one end of the fusible element, said borebeing provided witha longitudinally disposed slot in its side wall, a stud on the side wall of the plug which engages said slot while the plug is being inserted in or removed from the bore, said stud being connected to the other end of the fusible member, and a second contact element for said adapter arranged to be engaged by said stud when the inserted plug is rotated.

3. In an electric fuse, the combination of a receiving member provided with a cylindrical bore, said bore being provided with an arcuate seat formed in its inner wall and a longitudinal groove extending from the outer end of the bore to said seat, an electrical contact element positioned at the inner end of the bore and a second electrical contact member exposed in said seat but out of registration with said groove, a plug arranged to be inserted into said bore, a third electrical contact member at the inner end of the plug arranged to engage the first contact member, a fourth electrical contact member protruding laterally from said plug and adapted to pass down along said groove as the plug is inserted into the bore and to be brought into engagement with the second contact member by the rotation of the plug after it has been inserted into the bore, and a fusible element mounted on the plug and connecting the third and fourth contact elements. 

